This Class (Lecture 32): Cultural Evolution Next Class: Lifetime ET: Astronomy 230 HW 7 due today! Outline Will a civilization develop that has the appropriate technology and worldview? The most important worldview shift for humans was the Copernican revolution. From center of the Universe to not special. Music: Human Human League = 1.6 Intelligent Life # of advanced civilizations we can contact in our Galaxy today /decade Drake Equation N = R * f p n e f l f i f c L Rate of star formation 10 stars/ yr Fraction of stars with planets 0.38 systems/ star # of Earthlike planets per system 0.11 planets/ system Fraction on which life arises 0.5 life/ planet Fraction that evolve intelligence 0.75 intel. /life Frank Drake Fraction that communicate comm./ intel. Lifetime of advanced civilizations yrs/ comm. Our First View The first concepts of the Universe were Earthcentered. How did we come to this point Astro 230? First recorded cosmology was from the Babylonians. The Universe is a large oyster, and we are inside. But other aspects of their astronomy was advanced. Regularity of astronomy for crop planting, harvesting, and accurate calendars back to the 3800 BC. http://www.internationalenglish.co.uk/co urses.htm
Our First View Greek Astronomy The Mayans computed the length of year to within a few seconds (0.001%). So early humans had a weird mixture of precise calendar astronomy with primitive concept of the Universe and mythological systems incorporating magic. Greeks were excellent Astronomers Cataloged star positions & brightness. Systematic, quantitative observations. Natural philosophers. They observed that the stars, Sun, and planets revolved around the Earth. So Earth is center of Universegeocentric cosmology (mostly from Plato and Aristotle). Perfect Spheres of motion? http://www.mayasites.com/equinox.html http://ephemeris.com/history/mayan-calendar.jpg Mars Moves WRT the Stars! Motions of Planets E A S T W E S T So, over time the planets seem to move along the ecliptic from west to east over long time periods. This is called prograde motion But once in a while, a planet appears to stop and reverses direction Reverse direction is called retrograde motion (east to west). Planets move counter-clockwise (looking down at the north pole)
How can we explain the Planet motion? Ptolemy (140 AD: `p` is silent) With a geocentric cosmology you can t easily explain this retrograde motion of the planets. Note: perfect circles Took geocentric model with uniform circular motion to introduce the Ptolemaic system, or model, of the Solar System that could explained retrograde motion Ptolemaic system Ptolemaic system Geocentric Nice circular motion Yes, it can explain retrograde motions
Overall system of the Solar System. Ptolemaic system Ptolemy s Geocentric Cosmology: Is it a Scientific Theory? Yes! and an accurate one too Data: Sun/moon/star motions Tentative Model: circular orbits Prediction: uniform motion on sky New data: retrograde motion Refined model: epicycles explains data! http://home.comcast.net/~fsteiger/theory.htm Ptolemy s Geocentric Cosmology: Is it a Scientific Theory? Yes! and an accurate one too Data: Sun/moon/star motions Tentative Model: circular orbits Prediction: uniform motion on sky New data: retrograde motion Refined model: epicycles explains data! Result: Ptolemaic system (theory) Strength: accurate fit of data Weakness: predictions for new data? Ptolemaic Problems Each planet acted independently of others There was no universal rule governing the planets motions. Nonetheless, for a 1000 years this model ruled western thought However, by the late middle-ages astronomers felt that it was too complex, and a search began for a system with simple underlying principles http://gbgm-umc.org/umw/bible/images/ptolmai2.jpg http://www.tmdrfan.com/rthurlow/thomasdolby1982.htm
Lessons: Were the Greeks Stupid? Not at all! Developed sophisticated, successful model But built in prejudices about the world not just geocentric but egocentric What about scientists today? Still can fool ourselves! (And have!) But: scientific method is tool: To keep from fooling yourself To correct yourself when you have My guess: 70% of the material in this course will stand the test of time Compare baseball: 30% success good But also: 30% of course is wrong/incomplete! Which 30%? Don t know! Would fix it if we knew! So You have to learn all of it! http://www.farhorizon.com/europe/images/ima ges-greece/head_of_greek_god.jpg Power of Ignorance Geocentric model was absorbed by Christianity. If Geocentric, then of course no ET life. St. Augustine (420 AD) incorporated Neo-Platonism. He listed science as a temptation to avoid: a mere itch to experience and find out Also said, Nor do I care to know the course of the stars. http://www.flholocaustmuseum.org/history_wing/assets/room1/st._augustine.jpg Power of Ignorance The European worldview degenerated for years. No one in Europe mentioned the supernova of 1054 (Crab Nebula), unlike China or Americas. People were afraid to notice it and be described as a heretic. Could an ET civilization reach technology with that sort of attitude? http://www.pbs.org/deepspace/timeline/tl14.html http://www.godandscience.org/images/crabnebula.jpg Copernicus (1540) resurrected the heliocentric model If Earth moves, then stars have to be very far away. Was rejected on theological and philosophical grounds. 1616, the Church listed it as heresy. http://www.tulane.edu/~danny/southwest.html
Giordano Bruno Seems to have taken it one step further. Thought that the stars were all little Suns. Possibly with planets of their own. Maybe life on those other planets. Maybe more advanced than those on Earth. These are some of the reasons why he was burned at the stake around 1600. Can explain retrograde motion Much simpler Still kept to circular motion Eventually changed the way we think of ourselves! Copernican Theory Copernicus (1540) Heliocentric Model Tycho Brahe (1580): Uraniborg BUT, keep in mind that the geocentric model was still valid. Both models explained the observed motion. Accurate measurements to about 1 minute of arc (1/15 the diameter of the moon). No telescopes! Heliocentric is NOT obvious! IT was determined a philosophical argument for 50 years! New observations were required to determine which is correct.
Johannes Kepler (1600) Tycho s assistant in Prague After Tycho s death, succeeded Tycho s position and had access to the excellent data How to fit the Heliocentric model to accurate data of Mars? Circles didn t work. Ellipses! Kepler s 1 st Law: Orbits of planets are ellipses with the Sun at one focus a Orbits of planets are ellipses with the Sun at one focus Not a perfect circle, but ellipses with varying eccentricity. New Twist even the Sun isn t at the center of the solar system now. How does that change our view of the Universe and our place in it? Implications http://antwrp.gsfc.nasa.gov/apod/ap010101.html
Kepler s 2 nd law: The Line that connects the planet to the Sun sweeps out equal areas in equal time Kepler s 3 rd Law: The squares of the orbital sidereal periods of the planets about the Sun are proportional to the cubes of the orbital semimajor axes Planet P (yr) a (AU) P 2 a 3 Mercury 0.24 0.39 0.06 0.06 Venus 0.61 0.72 0.37 0.37 P 2 = a 3 aphelion perihelion So, planet moves faster at perihelion. Earth 1.00 1.00 1.00 1.00 Mars 1.88 1.52 3.5 3.5 Jupiter 11.86 5.20 141 141 Saturn 29.46 9.54 868 868 P x P = a x a x a Where P is in years and a is in AU. Kepler s Laws The farther away from the Sun, the longer it takes for the planet to orbit AND the slower it s average orbit speed. Galileo (1610) First to systematically use the telescope (but did not invent it). Moon has mountains and valleys Milky Way consists of faint stars Saturn is elongated Venus shows phases Jupiter has moons (now called Galilean moons) Wow! Big stuff. The moons of Jupiter did not orbit the Earth!
The Phases of Venus Could not be explained with the Geocentric model http://www.astro.ubc.ca/~scharein/a310/solsysex/phases/phases.html Galileo (1610) Disproved Ptolemaic system Rome bullied him into recanting (cleared in 1992) Now we understand the motions and the fact that the solar system MUST be Heliocentric, but now we need a reason why? Need something with predictive power. http://www.calvin.edu/academic/phys/observatory/images/venus/venusb.html Gave us a reason why-- GRAVITY. Developed fundamental laws of nature. Kepler s 3 rd law now became a way to probe the structure of the Universe! We are not the center of the Universe. In the 1920s, we realized that we are not the center of the galaxy, and that there are many other galaxies. Isaac Newton f c Development Given that an intelligent civilization exists, what is the likelihood that it can (technologically advanced enough) and will want to (knows astronomy and thinks that its chances are good) communicate? Cultural evolution to technology and worldview are essential components of f c Extra-somatic storage of info crucial. Technology and innovation quantum mechanics Copernican revolution played an important role. ET has to realize that they are not the center of the Universe and that there might be other life.
Are we typical? f c Development Is it inevitable fc = 100% or a fluke 1/10000? Remember civilizations come and go, but in general the gains (technology/worldview) aren t lost. Picked up by the next civilization. Even if one civilization goes dark for centuries, eventually another rekindles the technology/worldview.